The present invention concerns a method and apparatus for monitoring electrolyser performances and for diagnosing and predictive identification of faults and events likely to affect the manufacturing processes that uses those electrolysers.
An electrolyser is used to convert a lower value chemical (e.g.: NaCl) into a higher value chemical (e.g.: NaCl3O). These types of electrolysers can be found in different areas of the chemical industry, such as for the production of sodium chlorate, caustic soda and chlorine. In an electrolyser, there is a number of anodes and cathodes. An oxidation reaction takes place at the anode and a reduction reaction takes place at the cathode. The rate of chemical reaction is directly related to the current. An ion exchange membrane can be used to separate the anodic reaction from the cathodic reaction. The electrolysis of sodium chlorate is usually carried out in an undivided electrolyser. The overall reaction is described as: NaCl+3 H2Oxe2x86x92NaClO3+3 H2 
This reaction requires 6 electron per sodium chlorate produced. It involves a multi-step reaction, taking place at the anode and in the bulk of the reactor. The article from B. V. Tilak and C. P. Chen B. V. Tilak and C. P. Chen; xe2x80x98Electrochemical Society Proceedingsxe2x80x99; vol 99-21; 1999; pp.8; xe2x80x98Electrolytic sodium chlorate technology: current statusxe2x80x99 gives an overview of the technology. The electrolysis of chlorine and caustic soda can be achieved simultaneously in the same electrolyser. Caustic soda is formed is the cathode compartment. The chlorine is formed at the anode compartment. In modern chlor-alkali electrolyser, the separation between the anodic and the cathodic reaction is achieved with an ion exchange membrane. This membrane ideally only allows the passage of sodium from the anodic compartment to the cathodic compartment. The article from D. L Caldwell (D. L. Caldwell; Comprehensive Treatise of Electrochemistryxe2x80x99; Vol 2; 1981; pp 105; xe2x80x98Production of chlorinexe2x80x99; Editor: O""M. Bockris, B. E. Conway, E. Yeager and R. E. White; Publisher: Plenum Press, New York) gives more detail about this technology.
A fuel cell is a special type of electrolyser that is used as a generator. It converts the chemical energy of a fuel into electrical energy. Fuel cells are composed of a number of anodes and cathodes. It is at the anode that the fuel is electrochemically oxided and it is at the cathode that the oxidant is electrochemically reduced. Electrons are generated at the anode and flow through an external load to the cathode. Ions flow between the anode and the cathode in an electrolyte to complete the circuit. There are different fuel cell technologies. The proton exchange membrane fuel cell (PEMFC) is one of them. The PEMFC is also known as a solid polymer electrolyte (SPE) fuel cell. In such fuel cell, a thin proton exchange membrane has on one of its faces an anode and on the other a cathode. Hydrogen is fed to the anode and reacts to produce protons. These protons move to the cathode where they react with oxygen to produce water. The overall reaction is: H2+xc2xdO2xe2x86x92H2O
The ways the anodes and cathodes are connected differ according to the technology. The electrodes can be connected in parallel, in series or in a combination thereof.
One of the problems associated with the monitoring of the electrolysers is the extremely hostile conditions in which they operate. This makes data acquisition difficult and unreliable. Furthermore, it is essential to monitor these electrolysers in order to maximize the production rate and quality while still maintaining a minimal operating cost. Looking at the overall production performance does not allow the operator to discover that a unit cell is under-performing and should be changed. There is a growing need from the industry to be able to diagnose the plant on a macroscopic level as well as on an individual cell unit level in order to correctly assess the cause of any performance decrease and determine what is the more economic solution to deal with the problem so identified. Usually, a plant operator monitors the electrolysers by measuring manually the pertinent parameters as voltage and current. Then, the data records are sent to the plant engineer, and by using his expertise and different data analysis he can find the symptoms that may cause the faults. This procedure is time consuming and imprecise, especially when the faults symptoms are defined by a large amount of data. For this reason, it is useful to have a system that can automatically and accurately monitor the electrolysers and help to quickly identify the problems that can occur in such plants to increase the production performance.
Known in the art is U.S. Pat. No. 5,945,229, to General Motors Corporation entitled xe2x80x9cPattern Recognition Monitoring of PEM Fuel Cellxe2x80x9d. The CO concentration in the H2 feed stream to a PEM fuel cell stack is monitored by measuring current and voltage behaviour patterns from an auxiliary cell attached at the end of the stack. The auxiliary cell is connected to the same oxygen and hydrogen feed manifolds that supply the stack, and discharges through a constant load. Pattern recognition software compares the current and voltage patterns from the auxiliary cell to current and voltage signatures determined from a reference cell similar to the auxiliary cell and operated under controlled conditions over a wide range of CO-concentrations in the H2 fuel stream. However, one of the problems associated with this method is that the reference signature is taken at ideal operating conditions for a fuel cell. No allowance is made for the variation in the operational characteristics of the fuel cell during the life of the fuel cell.
Also known in the art is U.S. Pat. No. 6105149 to General Electric Company entitled xe2x80x9cSystem and Method for Diagnosing and Validating a Machine using Waveform Dataxe2x80x9d. In this patent, a method and a system are developed to diagnose faults in devices such as computed tomography or magnetic resonance imaging machines. The faults are diagnosed by analysing waveform data obtained from the machines. A database containing the faults symptoms and corresponding repair actions are used to build classification rules. These rules are used to analyze new waveform data.
U.S. Pat. No. 5,584,291 to Instrumentarium entitled xe2x80x9cMethod for recognizing and identifying emergency situations in an anaesthesia system by means of a self-organizing mapxe2x80x9d describes a method of identifying emergency situations in an anaesthesia system by measuring a plurality of variables associated with an anaesthesia delivery. The measurement values of the measured variables are formed into pattern vectors characterizing the instantaneous states of the system.
Other fault diagnosis methods applied in plants that uses electrolysers can be found in the following patents: U.S. Pat. No. 4,532,018 to Olin Corporation entitled: xe2x80x9cChlor-alkali cell control system based on mass flow analysisxe2x80x9d, U.S. Pat. No. 5,015,345 to Denora Permelec entitled: xe2x80x9cMethod for detecting defective ion exchange membrane in monopolar and bipolar electrolysersxe2x80x9d and European patent application EP1069636A1 to General Motors Corporation entitled: xe2x80x9cFuel cell stack monitoring and system controlxe2x80x9d.
It is an object of the present invention to provide a system and apparatus that gives valuable information relative to the performance of electrolysers in a chemical manufacturing plant and helps to diagnose the origin of performance fluctuations that sometimes occur during the production.
In accordance with the invention, this object is achieved with a method and apparatus for monitoring electrolyser performances and for diagnosing and predictive identification of faults and events that could affect the manufacturing processes that uses electrolysers. The system comprises:
a) a plurality of acquisition and transmission units, each of said acquisition and transmission units measuring a plurality of variables related to a respective electrolyser and for transmitting said variables;
b) a database and data management unit for recording the variables transmitted by each of said acquisition and transmission units;
c) an intelligent data analysis and fault diagnosis unit for analysing said variables and diagnosing events;
wherein each of said units are interconnected through a communication unit.
In accordance with a preferred embodiment of the invention, the system includes: a data acquisition and transmission unit which acquires parameters such as voltage, current and temperature from the cells. These convert the analog signals into digital data streams. Those data sets are concentrated and transmitted by the communication unit to the database and data management unit, which records and formats them into data rows files. A processing and monitoring unit that displays desired data trends and added value data, which are pre-processed and filtered based on a user-defined manner. In addition, the monitoring units displays alarms, recommended actions and generates reports. The data rows are fed to the monitoring unit from the database and management unit by making export requests to the communication unit. An intelligent data analysis and faults diagnosis unit tracks the evolution of defined pertinent parameters. This unit prevents faults and events before they occur by isolating data trends signatures. The plant engineer or the plant analysis lab defines these faults signatures in advance based on their experience or based on a prior knowledge for the characteristics of the electrolysers in the plant. All the units are constructed around the communication unit that simplifies the importing and exporting of data and information between the system units and a remote third party software or hardware through a network.